The mucosal immune system is constantly exposed to a wide range of commensal and potentially pathogenic microbial species. This chronic exposure to inflammatory mediators and nonpathogenic organisms makes generation of an appropriate immune response critical in maintaining a balance between elimination of harmful pathogens and regulating responses to nonpathogenic organisms. While Listeria monocytogenes (LM) (a category B Biodefense priority pathogen) is one of the most widely utilized pathogens for examining T cell immune responses, little is known about induction of the mucosal CD8 T cell response after oral infection. The overall hypothesis to be tested is that effector CD8 T cell subsets are differentially regulated by mucosal environmental cues to promote rapid local protection. We will address this hypothesis using a new oral infection model that more closely mimics the human infection. The specific aims of the project are: Aim 1: To define the anatomical events leading to generation of protective mucosal CD8 T cell memory. Aim 2: To understand the dynamics of CD8 T cell priming in response to oral bacterial infection. Aim 3: To define the mechanisms regulating development of protective mucosal CD8 memory T cells. The studies proposed will examine the eariiest events of CD8 T cell differentiation through memory T cell homeostasis and recall to secondary challenge. Examining the induction of effector T cells and the maintenance and recall of memory T cells to a bona fide gut pathogen that closely mimics human infection is critical for a better understanding of CD8 T cell immunity in the intestinal mucosa. The knowledge gained from this proposal has broad application potential ranging from understanding the immune response to intestinal pathogens to mucosal vaccine designs.